The present invention relates to a process for the preparation of 1-chloro-1-fluoroethane (HFA-151a) and/or 1,1-difluoroethane (HFA-152a), starting from vinyl chloride, performed in the liquid phase in an organic solvent.
It is known to prepare 1-chloro-1-fluoroethane by reaction between vinyl chloride and hydrogen fluoride in the liquid phase.
For example, in Patent DE 859,887, 1-chloro-1-fluoroethane is obtained by reaction between vinyl chloride and hydrogen fluoride, in the absence of catalyst, simply by introducing the reactants into an autoclave, in which they are heated moderately under autogenous pressure. This process leads, however, to the formation of a larger amount of oily side products.
U.S. Pat. No. 2,495,407 teaches the preparation of 1-chloro-1-fluoroethane starting from vinyl chloride in the presence of tin halide. In the various examples, the reactants are loaded into an autoclave with the desired amount of catalyst and are then subjected to a temperature close to 40xc2x0 C., under autogenous pressure. This patent also reports some unsuccessful attempts which were performed in the presence of acetic acid or acetone as solvent.
It has nevertheless been observed that these known processes lead to the formation, sometimes in very large amounts, of heavy halogen-containing side products which are mainly formed of oligomers of vinyl chloride, which partly contain fluorine. The formation of these side products seriously affects the reaction yields of 1-chloro-1-fluoroethane and of 1,1-difluoroethane. In addition, the clean destruction of these halogen-containing side products requires the implementation of difficult and very expensive techniques.
Patent FR 1,396,251 has proposed a process for the manufacture of halogen-containing derivatives of ethane, which avoids the unwanted formation of large amounts of heavy halogen-containing derivatives. To this end, a vinyl halide in the gaseous state is introduced continuously, at atmospheric pressure, into a reactor containing a liquid medium formed essentially of anhydrous hydrogen fluoride, maintained at a temperature between xe2x88x9215 and +19xc2x0 C. With the aim of accelerating the reaction or of reducing the vapour pressure of hydrogen fluoride, it is envisaged in this document to add to the hydrogen fluoride various acidic or inert substances which are miscible with the latter, in an amount by weight which is less than or equal to the amount of hydrogen fluoride. In the case where vinyl chloride is used, this known process gives rise to the joint production of 1-chloro-1-fluoroethane and 1,1-difluoroethane. However, this process appears to be of little practical value. It makes it necessary, in fact, to work with a large amount of hydrogen fluoride in the reactor, which involves acute safety problems. In addition, this process does not appear to be adapted to a variable production of 1-chloro-1-fluoroethane and 1,1-difluoroethane, which would be industrially exploitable.
The aim of the present invention is to overcome the abovementioned disadvantages of the known processes and to provide a process for the preparation of 1-chloro-1-fluoroethane and/or of 1,1-difluoroethane starting from vinyl chloride, which process is of high production efficiency and which allows the relative productions of 1-chloro-1-fluoroethane and 1,1-difluoroethane to be varied within a wide range, while limiting the unwanted formation of heavy halogen-containing side products.